At present, there are an estimated 140 thousand people with hemophilia worldwide, showing an annual increase of 20%. Genetically, hemophilia occurs in one out of every ten thousand, but diagnosis or treatment is made only for approximately 25% of all patients. Based on etiology, hemophilia is largely divided into two types: one is hemophilia A that is caused by a lack of blood coagulation factor VII (Factor VII, FacVII) and accounts for 80% of the total hemophilia patients, and the other is hemophilia B that is caused by a lack of blood coagulation factor XI (Factor XI) and accounts for 20% of the total hemophilia patients. For the treatment of hemophilia, external administration of blood coagulation factors is given, but this treatment method is problematic in that 10-15% of all hemophilia A patients develop antibodies against the blood coagulation factor, and 1-3% of all hemophilia B patients develop antibodies against the blood coagulation factor.
On the other hand, FacVII, which is a cause of hemophilia A accounting for more than a half of the hemophilia patients, is an enzyme that is mainly produced in the liver and composed of 406 amino acids, and includes gamma-carboxylation of glutamic acid at position 10, N-glycosylation of asparagines at positions 145 and 322, and O-glycosylation of serines at positions 52 and 60. Further, FacVII has two EGF-like domains and one serine protease domain, and single-chain FacVII is activated through cleavage between arginine at position 152 and isoleucine at position 153 to generate two-chain FacVIIa consisting of a light chain and a heavy chain. Since activated FacVIIa acts through auxiliary blood clotting mechanism, unlike other blood coagulation factors, antibodies are not produced even though injection of high-dose FacVIIa. Therefore, it can be used for the treatment of hemophilia A patients as well as patients having antibodies against FacVII due to the conventional therapies, and is known as a means of addressing the above described problems.
However, antibodies against FacVIIa are not produced, but there is another problem of requiring high-dose, frequent administration because of a short blood half-life. Because of the short half-life, FacVIIa should be administered 2-3 times a day for the treatment of hemophilia, and this frequent administration also becomes a serious obstacle to the prevention of hemophilia. In order to solve the problem of short blood half-life, studies have suggested the known microencapsulation, liposome encapsulation, and a variety of chemical modifications, but successful outcomes have not been reported yet. In particular, chemical modifications have been attempted such that the lysine residue or N-terminus on the surface of FacVIIa is chemically modified, or a carrier capable of extending blood half-life such as polyethylene glycol, albumin, transferrin, and immunoglobulin fragment is linked thereto, or a cysteine residue is inserted into a region not directly affecting the activity of FacVIIa to promote binding with other carrier. However, chemical modification of the lysine residue or N-terminus on the surface of FacVIIa reduces the ability of FacVIIa to bind with the membrane of platelet. When it is linked to other carrier, the carrier interferes with enzymatic activities. Insertion of cysteine residue induces formation of non-specific disulfide bond, consequently leading to a reduction in enzymatic activities. As such, many studies have been made to develop derivatives having an improved blood half-life without reducing the activity of FacVIIa, but no successful results have been reported yet.
rVIIa-FP (CSL Behring) prepared by fusion of albumin to the C-terminus of FacVIIa is in the pre-clinical phase, and its blood half-life in rats was increased to 6.7 times higher than that of the native FacVIIa. However, it still has a very short half-life of 4.38 hrs, and thus is not suitable for the treatment and prevention of hemophilia. PEGLip-FVIIa (Omri) prepared by using a pegylated liposome formulation is also in the pre-clinical phase, but its blood half-life was only 2 times higher than that of the native FacVIIa.
Two products, MAXY-VII (Bayer/Maxygen) prepared by Gla domain mutation and hyperglycosylation of FacVIIa to have a prolonged blood half-life and NN7128 (Novo/Neose) prepared by 40K PEG glycosylation to have a prolonged blood half-life are under clinical studies, but their blood half-life was only 5 times higher than that of the native FacVIIa. Thus, they are not suitable for the effective treatment and prevention of hemophilia.